1. Field of the Invention
The present invention relates to a spindle motor and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks are typically installed in hard disk apparatuses and optical disk apparatuses. Such a spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque by magnetic flux generated between a stator and a magnet, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary portion and the rotating portion of the spindle motor are joined to each other through a fluid dynamic bearing. A known spindle motor including the fluid dynamic bearing is described, for example, in JP-A 2006-158015. This known spindle motor includes an upper bushing and a lower bushing fixed to a shaft (See, for example, paragraph [0029] of JP-A 2006-158015). While the spindle motor is rotating, dynamic pressure grooves defined in an inner circumferential surface of a sleeve cause the sleeve to be out of contact with each of the upper and lower bushings (See, for example, paragraph [0034] of JP-A 2006-158015).
Regarding spindle motors in recent years, there has been a strong demand for a reduction in a magnitude of a drive current needed to obtain a desired rotation rate from the viewpoint of energy saving and environmental performance. The reduction in the value of the drive current can be achieved, for example, by arranging the fluid dynamic bearing at a radially inner position, where the moment is small and the circumferential velocity is slow, thereby reducing a friction loss at the fluid dynamic bearing.
However, a known spindle motor which includes a fluid dynamic bearing including a pair of upper and lower bearings each of which is inclined with respect to a central axis has a problem in that arranging both the upper and lower bearings more radially inward than before makes it difficult to rotate the spindle motor stably although a reduction in the friction loss at the fluid dynamic bearing is achieved.